class_docstr: Mesh implemented using explicit device placement.
code: def __init__(self, shape, layout, devices):
      super(PlacementMeshImpl, self).__init__(shape, layout)
      self._devices = devices
      self.copy_master_to_slice_ops = []
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import functools
  import os
  import random
  from mesh_tensorflow import ops_with_redefined_builtins
  from six.moves import xrange
  import tensorflow.compat.v1
label_desc: Use image node_id 1 to create a new PlacementMeshImpl object from inherited base classes: mtf with example: obj = PlacementMeshImpl(shape, layout, devices)